Polyester and polyester copolymer compositions include, inter alia, polylactic acid (PLA). Polylactic acid may be considered a, renewably sourced, a biodegradable and/or a biocompatible polymer, and belongs to a group of polymers known as aliphatic polyesters. In general terms, so long as the basic monomers (lactic acid) of polylactic acid are produced from renewable resources (e.g., sugar or other carbohydrates), polylactic acid can generally be classified as an environmentally friendly material.
The synthesis of polylactic acid is a multistep process, generally beginning with the production of lactic acid (monomer) and ending with various polymerization steps. To offer somewhat of an oversimplified summary, polylactic acid may be synthesized via condensation polymerization of lactic acid, which generally yields a low molecular weight polylactic acid. Alternatively, polylactic acid may be synthesized through a series of dehydrative condensation, depolymerization and ring opening polymerization reactions, which generally yields a high molecular weight polylactic acid. Nowadays, polylactic acid can be found available in a wide variety of industrial commercial grades.
The stereochemical structure of polylactic acid can be essentially modified by polymerizing a controlled mixture of L and D isomers to yield high molecular weight amorphous and/or semi-crystalline polymers.
Although polylactic acid has been afforded some attention in recent years as a relatively inexpensive polymer to make, as well as for certain properties which make polylactic acid suitable for wide variety of applications, the commercialization of polylactic acid is not without its own unique set of challenges and difficulties
More specifically, and in some ways independent of the processing methodology (e.g., injection molding, compression molding, extrusion molding, blow molding, foam molding, etc.), in order for certain polyester and polyester copolymer based compounds, such as polylactic acid, to be processed into a final product, it is useful to enhance or improve the thermal stability and/or hydrolytic stability prior to or post processing to prevent or minimize degradation, and maintain molecular weight and other properties.
In particular, polylactic acid is generally processed at temperatures ranging from about 175° C. to about 190° C., yet is also at risk of thermal degradation at temperatures greater than about 195° C. to about 200° C. As a result, this narrow processing window creates a need for approaches to improve the processability of polyester and polyester copolymer based compositions, such as polylactic acid.
Accordingly, approaches such as reducing the glass transition temperature of polylactic acid, increasing the molecular weight, viscosity and/or changes in acid value and/or hydroxyl value would be useful. The present disclosure addresses these and other needs by providing polyester or polyester copolymer based compositions, such as polylactic acid based compositions, having improved stability as described herein.